The roof is about 1502.6 ft², 15 roofing squares. Buy 50 bundles, 16.7 squares, to cover it with 10% waste.
15 roofing squares · plan 1344 ft² × 1.118. A square is 100 ft² (9.29 m²).
50 bundles at 3 per square, with 10% waste. Ridge cap, starter and underlayment are extra.
26.57° · multiplier 1.118.
$1.20 per ft² of roof. Shingles $1,800. Not a quote.
Type the building's footprint, the overhang and the pitch. This roofing calculator turns them into roof square feet, roofing squares and shingle bundles, for a gable, a hip roof or a shed. Add a bundle price and you get a sample cost. Run it before you order: a pallet short halfway through a tear-off is a bad day, and worse with rain coming.
Quick answer A 40′ (12.19 m) × 30′ (9.14 m) house with a 12 in (305 mm) overhang at 6:12 has 1502.6 ft² of roof, which is 15 roofing squares. Add 10% waste and you buy 16.7 squares: 50 bundles at 3 to the square.
Roof area is the footprint times the pitch multiplier. Every roof plane at the same pitch is stretched by the same factor, √(1 + (pitch ÷ 12)²), so a gable, a hip and a shed that share a footprint and a pitch have the same roof area. This roof area calculator adds the overhang first. Overhang is level distance, so it goes onto both sides of the length and the width, and the whole footprint gets multiplied.
A roofing square is 100 ft², the unit shingles are priced in, so a roofing square calculator just divides the roof area by 100. The roof sq ft figure comes first (square metres in metric). Shingles come in bundles, three to the square for most products. Waste is added to what you buy and not to the roof area, and the result is rounded up to a whole bundle.
Hips, valleys and dormers leave the area sum alone but raise the waste, because every hip, valley and cut edge sheds offcuts. That is why the waste hint steps from 10% on a plain gable to 15% on a hip roof. If part of the roof has a different pitch, run the calculator once per part and add the areas. The second section box takes a garage or wing at the same pitch.
The pitch sets the multiplier, so measure it first with the roof pitch calculator. The rafter length calculator works out the framing for the same roof, and the French drain cost calculator covers where the roof water goes once it hits the ground.
A = roof area, L × W = building footprint, o = overhang, p = pitch (the x in x:12).
multiplier = √(1 + (pitch / 12)²) pitch in x:12 plan area = (length + 2 × overhang) × (width + 2 × overhang) + second section roof area = plan area × multiplier squares = roof area in ft² / 100 bundles = ceil( squares × (1 + waste/100) × bundles per square ) squares to buy = bundles / bundles per square cost = bundles × price per bundle + roof area × labor rate
With a 12 in overhang the footprint grows to 42 × 32 ft, 1344 ft². The 6:12 multiplier is √1.25 = 1.118, so the roof is 1502.6 ft², 15.03 squares. Ten percent waste makes 16.53 squares, which is 50 bundles at three to the square, 16.7 squares in all. At $36.00 a bundle that is $1,800 of shingles.
A hip roof has the same area as a gable on the same footprint and pitch, so the sum does not change, but it has more hips and cut edges, so waste is 15%. The 18 in overhang makes the footprint 53 × 43 ft, 2279 ft². The 8:12 multiplier is 1.2019, which gives 2739 ft², or 27.4 squares. Buy 95 bundles, 31.7 squares.
The main block is 40 × 28 ft with a 12 in overhang and the garage wing is 24 × 22 ft, entered with its own overhang. At 5:12 the multiplier is 1.0833. The main block alone is 1365 ft², and with the wing the roof is 1937 ft², 19.4 squares. At 12% waste that is 66 bundles.
A 35° roof is 8.4:12, with a multiplier of 1.2208. The footprint with a 400 mm overhang is 9.8 × 7.8 m, 76.44 m², so the roof surface is 93.32 m². In shingle squares of 9.29 m² that is 10 squares, and with 10% waste 11.3. For tiles or slates, order by the square metre from the maker's coverage rate.
You do not have to climb the roof to take its measurements, and for safety you should not. The footprint, the overhang and the pitch give the area, and each one can be measured from the ground or the attic. This table lists what to measure and which field it goes into, so the roof calculator can do the rest.
| Measurement | How to take it | Calculator field |
|---|---|---|
| Building length | Wall to wall along the ground, measured level, outside face to outside face | Building length |
| Building width | The other side of the footprint, the full span, so both slopes of a gable are inside it | Building width |
| Overhang | How far the roof sticks out past the wall, measured level and not along the slope | Overhang |
| Pitch | Rise per 12 in of run from the attic, the plans, or a digital level reading in degrees | Pitch or Angle |
| Wings, garages and porches | Measure each the same way and include its own overhang | Second section |
| Pack size | Bundles per square, printed on the shingle pack | Bundles per square |
A fast way to sanity-check the calculator, or to size a roof from a plan. The first table is the footprint (the area of the building under the roof, overhang not included) at five common pitches, with no waste. The second is the bundles to buy for a roof of a given size at three bundles to the square, with the shingles priced at a sample $36 a bundle.
| Footprint | 4:12 | 6:12 | 8:12 | 10:12 | 12:12 |
|---|---|---|---|---|---|
| 1000 ft² | 10.5 | 11.2 | 12.0 | 13.0 | 14.1 |
| 1500 ft² | 15.8 | 16.8 | 18.0 | 19.5 | 21.2 |
| 2000 ft² | 21.1 | 22.4 | 24.0 | 26.0 | 28.3 |
| 2500 ft² | 26.4 | 28.0 | 30.0 | 32.5 | 35.4 |
| 3000 ft² | 31.6 | 33.5 | 36.1 | 39.1 | 42.4 |
| Roof area | 10% waste | 15% waste | Shingles at $36 a bundle, 10% waste |
|---|---|---|---|
| 10 squares | 33 | 35 | $1,188 |
| 15 squares | 50 | 52 | $1,800 |
| 20 squares | 66 | 69 | $2,376 |
| 25 squares | 83 | 87 | $2,988 |
| 30 squares | 99 | 104 | $3,564 |
| 40 squares | 132 | 138 | $4,752 |
Use this table as a roof replacement cost calculator for a first budget. A reroof cost calculator starts from the roof area, so every row runs the same sum as the calculator above, with a 12 in overhang, a 6:12 pitch and 10% waste. Shingles are priced at a sample $36 a bundle and labor at three example rates per square foot of roof, so the table shows how the total moves. It is not a quote. Tear-off, extra layers, access and your region all change the real price, so swap in your own bundle price and an installer's rate.
| House footprint | Roof area | Bundles | Shingles | Labor $3/ft² | Labor $5/ft² | Labor $8/ft² |
|---|---|---|---|---|---|---|
| 30 × 24 ft | 930.2 ft² | 31 | $1,116 | $3,907 | $5,767 | $8,558 |
| 40 × 30 ft | 1502.6 ft² | 50 | $1,800 | $6,308 | $9,313 | $13,821 |
| 50 × 30 ft | 1860.4 ft² | 62 | $2,232 | $7,813 | $11,534 | $17,115 |
| 50 × 40 ft | 2441.8 ft² | 81 | $2,916 | $10,241 | $15,125 | $22,450 |
| 60 × 40 ft | 2911.4 ft² | 97 | $3,492 | $12,226 | $18,049 | $26,783 |
Roof area is geometry. What the roof needs is set by the roofing chapter of the IRC and the shingle maker's instructions: minimum slope, underlayment, fastening and ventilation. Asphalt shingles are limited to slopes of 2:12 or more in IRC R905.2.2, with double underlayment between 2:12 and 4:12. Read the product listing and your local amendments. The IRC text is in IRC 2021 Chapter 9, Roof Assemblies.
A roofing square is 100 ft² of roof (9.29 m²). Three bundles to the square is the usual pack for three-tab and architectural shingles, but some heavier laminated shingles take four or five, so the label on the pack decides.
This calculator does not estimate ridge cap, hip cap, starter strip, drip edge, underlayment, flashing, vents or nails. Those are bought by the linear foot or the roll, and they depend on the details of the roof.
In the UK and much of Europe roofs are quoted in degrees and covered with tiles or slates by the square metre. Use the angle option and read the area in m². The bundle count is for shingles.
Working on a roof is dangerous. This page does arithmetic. It does not replace fall protection, a site check of the roof structure, or a roofer's measurement for a quote.
Section numbers refer to IRC 2021 section numbers; England Approved Document K. Local amendments are common, so confirm with your building authority.
Hover a question to read the answer. Click to keep it open.Tap a question to open it.
Add the overhang to both sides of the length and the width, multiply to get the footprint, then multiply by √(1 + (pitch ÷ 12)²). At 6:12 the multiplier is 1.118, so every 1,000 ft² of footprint is about 1,118 ft² of roof. The table on this page gives the squares for common pitches, and the roof pitch calculator has the multiplier for any pitch.
A roofing square is 100 square feet of roof. Most three-tab and architectural shingles are packed three bundles to the square, so a 20 square roof is 60 bundles before waste. Heavier shingles take four or five. Check the pack label and enter it in Bundles per square.
If 2,000 ft² is the footprint, a 6:12 roof is 22.4 squares before overhang and waste. A two-storey house has a smaller footprint than its floor area, so measure the building on the ground, not the floor area on the listing.
10% covers a plain gable. Go to 15% for a hip roof, several valleys or dormers, because each one leaves offcuts, and a very cut-up roof can need more. Waste is added to the amount you buy, not to the roof area, and this roof shingle calculator rounds up to a whole bundle.
Yes. The overhang is roof you cover with shingles, so add it to every side of the footprint before you multiply by the pitch factor. Enter the level overhang, not the length along the slope. Leave it out and a 12 in overhang on a 40 × 30 ft house understates the roof by about 11%.
Take three roof measurements from the ground and the attic: building length and width, wall to wall and level, the overhang past the wall, and the pitch. A hip, a valley or a dormer does not change the area sum, only the waste, so use 15% or more. Measure a wing or garage the same way and enter it as the second section.
Open Sample prices and enter the price per bundle from the pack or the quote, plus an installer's rate per square foot with tear-off and disposal in it. Then it works as a roofing cost calculator: bundles times price, plus labor on the roof area. The cost tables on this page run the same sum for common house sizes. It is a planning figure, not a quote, and underlayment, flashing and ridge cap are extra.
Ridge and hip cap, starter strip, drip edge, underlayment, flashing, vents and nails. Those are sold by the linear foot or the roll, and a roofer measures them on the roof. The calculator covers the field of the roof, the main shingle quantity.